Brushing or bead blasting necessary before powder coating?

[tysseng]

Should I apply brushing or bead blasting to a job if i add powder coating, given that I have selected a material that will oxidize, such as non-stainless steel?

[Tech2]

Not necessary.

[CMIndustries]

I have a question that falls under this same titlel. I am planning on making some guitar pick guards out of cast aluminum, with a powder coat finish. I realize that pre finishing is not necessary for the powder coat; what I need to know is what kind of surface cast aluminum has. Is the surface rough enough to warrant a mechanical finish for cosmetic improvement? I have had satin buff polished parts (T5 Aluminum) come with some ugly scratches, and can't have that on these; I need them to have a very finished look. Also, is mechanically finishing the top and bottom surfaces with an orbital sand or mechanical brushing necessary to get rid of any residual flashing from the casting process?
Again, these parts need to look very "clean."
Thanks!

[Tech2]

You would not want to cast. I presume the pick is flat. I suggest to design it as a 2D part and indicate to tumble to round edges. That with powder coat should work.

[CMIndustries]

Yes it is flat, but it is a pick guard, 8 inches x 10 inches, so I imagine that tumbling would be impractical. I will take your advice anyhow, and will probably have them done in T6 aluminum.
Now, I know that with the T6 I can just specify a surface roughness and have the Auto machine do it however it pleases, but I need to know what a 63 microinch surface finish looks like. What are the approximate surface roughnesses of the attached pics? I like the surface of your machinists’ rulers that you send out with customer orders also, but I imagine that is more like a 32 microinch or finer finish?
Thanks!

[Tech2]

Those look to be in the 16 or 32 range.

[CMIndustries]

OK, so a buff polish is needed then. The CAD software says that both buff polishes (satin and mirror) have a finish quality in the 1 micro-inch range, which seems off, (too fine???) but hopefully I am wrong.

So basically, If I were to do the parts in T6 Aluminum, buff polish (mirror) them, and glossy powder coat them, I would end up with a very high quality, scratch less, (as in the previous pictures) surface, correct?

Thanks again.

[Tech2]

Surface Ra of 125 is all you need under powder coat and will keep your cost down.

[CMIndustries]

Oh wow, the powder coat will hide that much? The CAD implies that only the textured powder coat has decent imperfection alleviation...again, that is my main concern here, a very smooth surface. Sounds like the glossy powder coat will take care of that.

Anyway, cool! That does keep the cost way down.
I will probably go that route.
Thanks a bunch, you guys rule!

[Tech2]

Surface roughness 125 is 125 millionths of an inch. That's about 0.1 thousandths. Powder coat is typically a few thousandths.

[CMIndustries]

Awesome! Thanks again!